Loaded antenna

Abstract: A loaded antenna which can be extended for use and retracted for storage, for use on a portable radio communication device, comprising: a feeding point member for supplying a signal to be transmitted; a loading coil having one end electrically connected to said feeding point member; and a whip antenna disposed for movement between an extended position in which the whip antenna is electrically connected to the other end of said loading coil, and a stored position in which the whip antenna is electrically disconnected from the other end of said loading coil.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a loaded antenna for use on a portable radio communication device. Description of the Related Art: Recent years have seen widespread use of portable radio communication devices such as portable telephone sets. Such portable radio communication devices are required to be small in size and light in weight, and have antennas that are extended when in use and stored when not in use. On small-size portable radio communication devices, the antenna is positioned closely to those components, including the housing of the device and the printed-circuit board in the housing, which affect the characteristics of the antenna. When the antenna is stored, it is positioned in the housing closely to the printed-circuit board, resulting in a reduced antenna gain. During storage of the antenna, the gain of the antenna is also lowered because the effective length of the antenna is smaller. To meet the requirements for small sizes and low weights, there have been demands for portable telephone sets, cordless telephone sets, and low-power radio communication devices which have smaller and lighter circuit components and batteries, and smaller and higher-performance antennas. Generally, portable radio communication devices are designed to radiate a predetermined amount of electric energy while the antenna is being extended. The user of a portable telephone set extends its antenna before making an outgoing call through the portable telephone set. However, when an incoming call from another party arrives, the antenna has usually been stored in the housing of the portable telephone set. Upon arrival of the call, the user extends the antenna for use. More specifically, when a portable telephone set receives an incoming call from a central office, it is necessary for the portable telephone set to transmit a response signal to the central office in response to the incoming call for the purpose of confirming a telephone connection that has been established between the central office and the portable telephone set, so that a ringing tone can be generated indicating the incoming call to the user. When the antenna of the portable telephone set is stored at the time the incoming call arrives, however, since the gain of the antenna is lowered, the electric energy radiated from the antenna is of a low level. If the portable telephone set is distant from the central office, then the response signal which is transmitted from the portable telephone set in response to the incoming call may not reach the central office, and the portable telephone set may not generate a ringing tone. Therefore, since the characteristics of the storable antennas arc degraded when the antennas are in storage, it has been desired to mechanically improve the characteristics of the storable antennas. Heretofore, most portable telephone sets employ whip antennas. Attempts to make portable telephone sets smaller in size have also resulted in the use of planar antennas, top-loaded antennas, small-sized whip antennas, and bottom-loaded antennas. The bottom-loaded antennas have find use as fixed antennas, but have not been used as antennas that can be retracted or contracted for storage. In "Motorola Technical Developments No. 19 (June 1993) by James T. Wiggenhorn" there is a proposal for an antenna including a central loading coil between an upper and a lower conducting metal sleeve. A telescopic member in a collapsed position nests co-axially within the metal sleeves. In this position the device acts as a helical antenna. When the telescopic member is extended its lower end shorts out the central loading coil and the device acts as a whip antenna. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a bottom-loaded antenna for use on a portable radio communication device, the bottom-loaded antenna being operable as a loaded whip antenna when extended and as a helical antenna when stored. Another object of the present invention is to provide a loaded antenna for use on a portable radio communication device, the loaded antenna being mechanically switchable to different loading coils when the antenna is extended and stored. According to a first aspect of the present invention, there is provided a loaded antenna device for use on a portable radio communication device, comprising a feeding point member for supplying a signal to be transmitted; and a whip antenna disposed for movement between an extended position and a stored position characterized in that the device further includes a bottom loading coil having one end electrically connected to said feeding point member; that in the extended position the whip antenna is electrically connected with one end to the other end of said bottom loading coil; that in the stored position said one end of the whip antenna is electrically disconnected from the other end of said bottom loading coil; and that the device also includes a top loading coil electrically connected to the other end of said whip antenna, said top loading coil being disposed for electrical connection to the other end of said bottom loading coil when said whip antenna is in said stored position and for electrical disconnection from the other end of said bottom loading coil when said whip antenna is in said extended position. Optional features of the embodiments according to this aspect of the invention are defined in claims 2 to 3 below. When the whip antenna is extended, it operates as a loaded antenna with the top and bottom loading coils. When the whip antenna is not extended, it operates as a helical antenna. According to a second aspect of the present invention, there is provided a loaded antenna device for use on a portable radio communication device, comprising a feeding point member for supplying a signal to be transmitted; a whip antenna disposed for movement between an extended whip position in which the whip antenna is electrically connected to said feeding point member, and a stored position; characterized in that the device further includes an extension loading coil electrically connected to said whip antenna; and a storage loading coil disposed for electrical connection to said feeding point member when the whip antenna is in said stored position. Optional features of the embodiments according to this aspect of the invention are defined in claim 5 below. When the whip antenna is extended, it operates as a top-loaded antenna. When the whip antenna is not extended, it operates as a helical antenna. The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary elevational view, partly in phantom, of a loaded antenna; FIG. 2 is a diagram showing the directivity pattern of a dipole antenna; FIG. 3 is a diagram showing a downward directivity pattern; FIG. 4 is a diagram showing the directivity pattern of a helical antenna; FIG. 5 is a fragmentary elevational view, partly in phantom, of a loaded antenna according to the present invention; FIG. 6 is a schematic view of the loaded antenna shown in FIG. 1 as it is installed on the portable radio communication device; FIG. 7 is a fragmentary schematic view, partly in cross section, of another loaded antenna according to the present invention, the loaded antenna being shown as extended; and FIG. 8 is a fragmentary schematic view, partly in cross section, of the loaded antenna illustrated in FIG. 7, the loaded antenna being shown as stored. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For comparison with the present invention a loaded antenna is shown in FIG. 1. The loaded antenna is shown extended. The loaded antenna, generally designated by the reference numeral 60, has a cylindrical feeding point member 61 which has a step on its bottom serving as a feeding point for supplying an electric energy to be transmitted from the loaded antenna. The loaded antenna 60 includes a tubular casing 62 threaded over an externally threaded portion 61a of the cylindrical feeding point member 61. The casing 62 has an attachment flange 62a on its upper end which will be attached to the housing of the portable radio communication device. The casing 62 houses therein a tubular loading coil support 63 of an insulating material which is fixedly mounted on an upper end of the cylindrical feeding point member 61. Between the tubular loading coil support 63 and casing 62, there is defined a concentric cylindrical space that accommodates a spring-like loading coil 64 disposed around the tubular loading coil support 63. The loading coil 64 has a lower end electrically connected to the cylindrical feeding point member 61. The loading coil 64 has an upper end fixedly connected to a substantially ring-shaped antenna element joint 66 which is disposed on the upper end of the tubular loading coil support 63. The antenna element joint 66 is made of an alloy of copper and nickel or the like. The antenna element joint 66 is electrically connected to the upper end of the loading coil 64. A whip antenna feeder 67 is vertically movably disposed in the tubular loading coil support 63. The whip antenna feeder 67 comprises a stepped cylindrical member made of an alloy of copper and nickel or the like. A whip antenna 69 has a lower end fixed to the upper end of the whip antenna feeder 67, and is electrically connected thereto. The whip antenna 69 may comprise a piano wire, a rod of a shape memory alloy, or the like. The whip antenna 69 is covered with an insulating protective layer 68 molded of synthetic resin. When the loaded antenna 60 is extended, i.e., when the whip antenna 69 is drawn upwardly, the whip antenna feeder 67 is brought into electric contact with the antenna element joint 66. As a result, the cylindrical feeding point member 61, the loading coil 64, the antenna element joint 66, the whip antenna feeder 67, and the whip antenna 69 are electrically connected to each other, whereupon the loaded antenna 60 serves as an ordinary bottom-loaded antenna. When the loaded antenna 60 is stored, i.e., when the whip antenna 69 is retracted downwardly, the whip antenna feeder 67 is lowered out of electric contact with the antenna element joint 66 into the tubular loading coil support 63. The cylindrical feeding point member 61 is now connected to only the loading coil 64, so that the loaded antenna 60 serves as a helical antenna. Characteristics of the loaded antenna 60 will be described below. FIG. 2 shows the directivity pattern of a dipole antenna. The antenna of the portable radio communication device is relatively short because the portable radio communication device has a small size. Therefore, the antenna of the portable radio communication device has a downward directivity pattern as shown in FIG. 3 and a low antenna gain. FIG. 4 illustrates the directivity pattern of a helical antenna which is placed on an ideal ground plane. The directivity pattern of the helical antenna is directed upwardly as shown in FIG. 4. When the loaded antenna 60 shown in FIG. 1 is extended, it operates as a bottom-loaded antenna, and its antenna gain and directivity pattern are not degraded though it is relatively small in size. The loaded antenna 60 as it is extended and serves as a bottom-loaded antenna has a directivity pattern which is substantially the same as the directivity pattern shown in FIG. 2. When the loaded antenna 60 is stored, it operates as a helical antenna and has a directivity pattern which is substantially the same as the directivity pattern shown in FIG. 4. At any rate, the loaded antenna 60 does not have the directivity pattern shown in FIG. 3. FIG. 5 shows a loaded antenna 70 according to the present invention, which may be used on the portable radio communication device. Those parts shown in FIG. 5 which are identical to those shown in FIG. 1 are denoted by identical reference numerals, and will not be described in detail below. The loaded antenna 70 illustrated in FIG. 5 differs from the loaded antenna 60 shown in FIG. 1 in that the whip antenna 69 has a top loading coil feeder 71 and a top loading coil 72 in an upper end portion thereof. The loading coil 64 shown in FIG. 5 is referred to as a bottom loading coil 64. The top loading coil feeder 71 is positioned on the top of and electrically connected to the whip antenna 69, and the top loading coil 72 is disposed above and electrically connected to the top loading coil feeder 71. When the loaded antenna 70 is extended, the cylindrical feeding point member 61, the loading coil 64, the antenna element joint 66, the whip antenna feeder 67, the whip antenna 69, the top loading coil feeder 71, and the top loading coil 72 are electrically connected to each other. The loaded antenna 70 now serves as an ordinary loaded antenna that is equipped with the top loading coil 72 and the bottom loading coil 64. When the loaded antenna 70 is stored, the whip antenna feeder 67 is lowered out of electric contact with the antenna element joint 66 into the tubular loading coil support 63, and the top loading coil feeder 71 is brought into electric contact with the antenna element joint 66. The cylindrical feeding point member 61 is now connected to only the bottom loading coil 64, so that the loaded antenna 60 serves as a helical antenna. Therefore, the bottom loading coil 64 and the top loading coil 72 are electrically connected to the cylindrical feeding point member 61, whereupon the loaded antenna 70 serves as a helical antenna. Consequently, the loaded antenna 70 operates as a loaded antenna when it is extended, and as a helical antenna when it is stored. The loaded antenna 70 has antenna characteristics that are fundamentally the same as those of the loaded antenna 60 shown in FIG. 1. The bottom loading coil 64 of the loaded antenna 70 may be smaller in size than the loading coil 64 of the loaded antenna 60. FIG. 6 schematically shows the loaded antenna 60 shown in FIG. 1 as it is installed on the portable radio communication device. As shown in FIG 6, the loaded antenna 60 is installed on a housing 80 of the portable radio communication device. In the portable radio communication device, a transmitter 81 and a receiver 82 are connected to an antenna sharing unit 83 which is connected through an antenna matching circuit 84 and a antenna feeder 85 to the loaded antenna 60. The loaded antenna 70 shown in FIG. 5 may be installed on the housing 80 and connected to the portable radio communication device as shown in FIG. 11. FIGS. 7 and 8 schematically show another loaded antenna according to the present invention as it is installed on the portable radio communication device. The loaded antenna being shown as extended in FIG. 7, and as stored in FIG. 8. In FIGS. 7 and 8, the portable radio communication device, designated by the reference numeral 90, has a ring-shaped feeding point member 91 disposed in a housing thereof. The loaded antenna has a whip antenna 93 connected at a lower end thereof to a cylindrical extension contact 92 and covered with a protective layer 94 molded of synthetic resin. The whip antenna 93 is vertically movable through the ring-shaped feeding point member 91. When the loaded antenna is extended as shown in FIG. 7, the cylindrical extension contact 92 is fitted into and electrically connected to the ring-shaped feeding point member 91. The whip antenna 93 has an upper end connected to the lower end of a connector 95, which has an upper end joined to an extension loading coil 96. The portable radio communication device has a transmitter 102 and a receiver 101 which are connected to an antenna sharing unit 103 that is connected through an antenna matching circuit 104 to the ring-shaped feeding point member 91. Therefore, when the loaded antenna is extended, the ring-shaped feeding point member 91 is electrically connected to the whip antenna 93 and the extension loading coil 96. The loaded antenna thus serves as a top-loaded antenna. A tubular storage contact 97 is fitted over the upper end of the protective layer 94, and electrically connected through a connector 98 to a storage loading antenna 99 which is disposed around the connector 95 below the extension loading coil 96. When the loaded antenna is stored as shown FIG. 8, the cylindrical extension contact 92 is lowered out of electric contact with the ring-shaped feeding point member 91, and the tubular storage contact 97 is lowered into electric contact with the ring-shaped feeding point member 91. As a consequence, the ring-shaped feeding point member 91 is electrically connected to only the storage loading antenna 99, whereupon the loaded antenna serves as a helical antenna. Generally, it is ideal for the antennas, including loading coils, of portable radio communication devices to have an effective length of λ/2 when extended and an effective length of λ/4 when stored where λ is the wavelength of radio waves that are transmitted from and received by the antennas. Accordingly, the length of the whip antenna 93, the number of turns of the extension loading coil 96, and the number of turns of the storage loading coil 99 may be determined to meet the above requirements. The loaded antenna according to the present invention operates as a loaded antenna when extended and as a helical antenna when stored. Thus, the loaded antenna maintains desired antenna characteristics even when it is stored. When the loaded antenna is stored, the desired antenna characteristics can also be maintained because the loaded antenna is mechanically switchable to different loading coils when the antenna is extended and stored.

Claims: A loaded antenna device (60; 70) for use on a portable radio communication device, comprising a feeding point member (61) for supplying a signal to be transmitted; and a whip antenna (69) disposed for movement between an extended position and a stored position; characterized in that a bottom loading coil (64) is provided which has one end electrically connected to said feeding point member; said whip antenna (69) in the extended position with one end is electrically connected to the other end of said bottom loading coil, and in the stored position said one end of the whip antenna (69) is electrically disconnected from the other end of said bottom loading coil (64); and a top loading coil (72) is provided which is electrically connected to the other end of said whip antenna (69), said top loading coil (72) being disposed for electrical connection to the other end of said bottom loading coil (64) when said whip antenna (69) is in said stored position, and for electrical disconnection from the other end of said bottom loading coil (64) when said whip antenna (69) is in said extended position. A loaded antenna device according to claim 1, further comprising a loading coil support (63) of an insulating material, said bottom loading coil (64) being fixedly mounted on said bottom loading coil support; an antenna element joint (66) mounted on an end of said bottom loading coil support and electrically connected to the other end of said bottom loading coil; and a whip antenna feeder (67) electrically connected to said one end of said whip antenna (69), said whip antenna feeder being movably disposed for electrical connection to said antenna element joint when said whip antenna (69) is in said extended position and for electrical disconnection from said antenna element joint when said whip antenna (69) is in said stored position. A loaded antenna device as claimed in claim 2, wherein said top loading coil (72) is connected to said other end of said whip antenna (69) through a top loading coil feeder (71) being movably disposed for electrical connection to said antenna element joint (66) when said whip antenna (69) is in said stored position and for electrical disconnection from said antenna element joint when said whip antenna (69) is in said extended position. A loaded antenna device for use on a portable radio communication device, comprising a feeding point member (91) for supplying a signal to be transmitted; and a whip antenna (93) disposed for movement between an extended position in which the whip antenna (93) is electrically connected to said feeding point member (91), and a stored position; characterized by an extension loading coil (96) electrically connected to said whip antenna (93); and a storage loading coil (99) disposed for electrical connection to said feeding point member when the whip antenna (93) is in said stored position. A loaded antenna device as claimed in claim 4, further comprising an insulating layer (94) covering said whip antenna (93); an extension contact (92) electrically connected to said whip antenna (93), said extension contact (92) being movably disposed for electrical connection to said feeding point member (91) when the whip antenna (93) is in said extended position; and a storage contact (97) fixedly mounted on said insulating layer (94), said storage contact (97) being disposed for electrical connection to said feeding point member (91) when the whip antenna (93) is in said stored position; wherein said storage loading coil (99) is electrically connected to said storage contact (97).

Inventors: HANAWA TETSUYA, KUGA YUJI, MATSUMOTO YOSHIHIRO, ONO MASAYUKI, TAKASHIMA YUTAKA, HANAWA, TETSUYA, KUGA, YUJI, MATSUMOTO, YOSHIHIRO, ONO, MASAYUKI, TAKASHIMA, YUTAKA
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1994
Main classification: H01Q1
IPC codes: H03G3, H01Q1